Lack of Power BELOW 3500 RPM.

when the bike is cold. she runs ALMOST like a champ. but as it warms up. it holds back on power BELOW 3500. she's perfect ABOVE 3500.

when it's cold i can romp on it a little. there's just a noticeable improvement at 3500. but when it's warm. it's almost like a turbo kicking in. in first gear. the higher the gear the more it struggles once it's warm.

she's not missfiring. just holds back. the warmer it gets, the worse it gets.

it also has a problem on the freeway. somewhere around 65 mph. it struggles to go any faster.

i've cleaned the carbs. set the floats at 16mm and now it's 14mm. at the base of carb. (float bowl contact, not the lip). one of the floats was sitting at 20mm. the other 3 were at 13mm ORIGINALLY. replace the fuel filter. fuel switch vacuum line was loose. and one vacuum cap was loose. swapped out for new parts. changed the spark plugs. gapped at .028 in. changed the fuel filter, and went through the fuel switch.

i haven't checked the compression yet. i'm also wondering if maybe plugged mufflers. but that should effect ALL tempuratures.

i'm wondering about the spark iginition system too. one of the components maybe? i don't think it would one of the coils. as the problem is temperature related.

ANY SUGGESTIONS. i can live with it the way it is around town. but running like a champ is the preferable solution for me. specially on them highway rides. where the speed limits is 75mph.

 

Well, since there is nothing about which bike you have...........

In general you're probably rich. Rich mixtures run better cold but start to fall down when the motorcycle warms up. Are your plugs all black and sooty?

The float heights you're throwing around sound like Hitachi carburetors (I don't think you can get a MIC down to 14mm). At 14mm dry height it'll let fuel trickle into the carburetor throat.

Bottom line:

1 - carburetors squeaky clean
2 - float height at the proper level
3 - mixtures properly set

 

i thought this was the maxim forum. LOL. it's an 81 650.

there's no difference in performance with floats set at either 14 or 16mm. and no difference in air/fuel adjustment. and i beleive the specs called for mikunis.

drove it again last night. turns out there's no difference between cold and hot. it's just not noticeable in first gear. second gear and higher is noticeable. the higher the gear the more noticeable the problem.

after sleeping on it. i'm starting to think it's a spark related problem. weak signal under 3500 rpm. and over 6000 rpm. which would explain the struggling on freeway. my speedo is slow so i'm not sure what my speed is. but i'm thinking 6000 is close to 70 mph. my top speed if i'm lucky.

anything under 3500 and over 6000 i'm getting a weak spark for some reason. anything IN the range and she runs like a champ.

least, that's what i'm thinking. ignition related problem

 

http://xjbikes.com/Forums/viewtopic/t=2 ... oting.html

bike all stock? original fuse box? Welcome to the site, you should put your bike in your signature and your location. looking at your local highway speed limit you're probably not near me lol. how were your diaphrams, pinholes etc...?

 

fuel system is perfect. nothing to diagnose. all clean and adjusted, cept for a carb sync. when i bought this bike the problem was really really bad. first gear even sucked. at first i thought it actually WAS a turbo. so, the problem is actually much better now. just still exists.

fuel is perfect. so i can't blame that. the guy i bought it from even replaced the boots. both front and rear. so those are all brand spanking new. it has to be something else. not related to fuel. to be honest, i would say the mufflers. cept that it runs like a champ between the specified rpm's.

EDIT: as far as the fuse box goes. looks like 2 of the fuses have been replaced. the main fuse has a replacement fuse connector but isn't mounted in the box anymore. the headlight fuse has been bypassed. wires are connected with no fuse now. will have to fix that dilemma.

 

It's not very likely to be ignition-related. It could be, but it's probably not. Check MiCarl's post again. You have the same problems as scores of other people with old bikes--believe him (and everyone else here), he would know. It's extremely likely that you have carb problems.

I have had very similar problems with my bike when I thought the carbs were clean, but they weren't clean enough.

That being said, I won't dismiss your thought that it could be electrical, since there are gremlins in the wires of my bike. I would always check the battery first. This seems to be the #1 source of problems on my bike (not now, but in the past). If it's not that, but you still think it's electrical, I would clean every connector on the thing with a steel brush and contact cleaner. That seems to work wonders too.

 

well, i've taken every jet out blown carb cleaner through every orifice and blown air and nothing is plugged up. carbs were already cleaned. and synced. but i went through and double checked. even tried screwing around with the air fuel screws. nothing seems to do any better. not even different float settings.

NOW, the guy may have changed main jets or idle jets. MAYBE even adjusted the needle in the sliders, if that's possible. i don't know. i don't have a book to gaurantee everything is correct. all i can say is nothing wrong with the carbs. and i've done quite a few bikes in my driving days. so this isn't my first rodeo.

if it's a air fuel mixture problem. i'm all out of ideas.

 

ready for this one? the air jets may be installed backwards. the pilot is the larger # and should be towards the front of the bike. They are both located under the diaphram on the upper part of the carbs. Let us know

 

i took the #2 cap apart. the large one was in the front. haven't done the rest yet. #2 didn't seem to have much of an effect as the other 3 cylinders when the spark plus was disconnected.

i did take her for a spin today. 60 miles. going up parleys canyon. which is on I-80 leaving east out of salt lake city. it's a very good climb. by the time i got to the top and got off the exit to turn around and come back. the motor was hot enough that even in first gear. acceleration was a pain untill i hit that magic rpm. by the time i got back in the city. the motor was cool enough to live with the problem again.

by the time i got back to the house. it seemed like the problem was much better. the turbo effect was gone and i actually had acceleration in 4th gear. the problem seems to have dropped down to about 1500 rpm now.

the guy i bought it from said he did have the valves adjusted. i'm starting to wonder if maybe the adjustment is too tight. hopefully a few miles of wear and tear might cure the problem.

CROSSING FINGERS. gonna take her for a mountain ride tomorrow. so we'll see what happens.

i'm hoping it gets better. cuz today's ride was only 60 miles and i used 2 gallons of gas. makes it hard to do any decent rides without a gas station at that rate. LOL.

 

-CHECK AND ADJUST VALVES. "PO said he had it done" is not good.

-Float heights need to be set using fuel and clear tubing, carbs dead level; "dry" setting is only a starting point.

-Carbs MUST be vacuum sync'ed or the bike will never ever run right. Bench sync first.

-Only after all of the above has been attended to do we start tweaking on mixture screws.

-Miles on bike? Pods, aftermarket exhaust, or all stock?

 

kinda hard to sync the carbs when the bike ain't running right first hand. synchronization mostly effects how smooth the idle is. shouldn't effect high rpms whatsoever. unless the throats are way outta whack then youi'd have surging rpm's.

so i did a compression check. gots 140 lbs on all 4 cylinders. BUT, #2 plug was whiter then casper. #3 had a somewhat tannish color. #1 and #4 are black. so looks like tearing down the carbs ONCE more. compare ALL the jets with 2 and 3 between 1 and 4. 2 and 3 has to have something wrong that 1 and 4 have right. OR, one of the coil packs OR the two plugs are running way hotter then they should. EITHER WAY, 2 and 3 are the problem childs for some reason

EDIT: #2 easily solved. vacuum line popped off for fuel switch. now it's black. #3 still golden in color.


if there is anyone with a manual that might have the numbers to the jets so i can confirm everything is the right stuff in the right holes. it would be greatly appreciated. teh top cap jets all have the bigger hets towards the front. have to clean em up to read the numbers.

 

yamaman. i can't really see the numbers on the jets. but i can tell you this. the bigger holed jets are defenitly in the front. does a bigger hole mean a higher number or lower number. cuz i'm starting to wonder if those two jets on top are backasswards.

can anyone confirm the bigger holed jet in the front????

EDOT: nevermind. i found someone on this forum with his own thread of pics of complete teardown. he's got the bigger one in front.

SO NOW I'M CLUELESS AS TO WHERE TO GO.

 

- check that all the jets are the same size by recording and comparing the #'s.
- maybe there' a crack that you can't see in the intake boot
- plugs all the same?
- throttle shaft seal corroded?
- maybe the fuel rail tube (that connects the carbs together) has build up on the inside of the walls restricting the flow to a point where it can't keep the flow the engine demands? never heard of that but just thinking in terms of what could make one cylinder lean

 

this guy replaced ALL the boots. both front and rear. and that wasn't cheap. LOL

i've changed the plugs. he had ngk's but the application number was for a porsche.

don't kow about the throttle shaft seal. will check next time i pull em apart AGAI N. sometime before the weekend.

 

you know. ii'm thinking about this carb situation. and i was thinking about something here. it don't matter if it's sitting still or running along in 5th gear. 3500 is when it kicks in 100 percent.

when the bgike is sitting still. the throttle is barely open. but in 5th gear. that's quit a bit of throttle. meaning the air fuel mixture has to be quite a bit different between stand still and 5th gear.

i can see a carb problem. but what, remains a mystery. but i would think there should be some type of difference between stand still and 5th gear. cuz that's different throttles at each instance.

i'm really starting to wonder if the problem isn't that igniter unit. cuz it don't matter how much throttle is being used or what gear it's in. 3500 is what it takes to run like a champ. and i mean 3500 EXACTLY. up to 6000 EXACTLY. and once in awhile, it does run better in a lower range.

 

You will be continuing to wonder what the problem is with no results until you sync your carbs and adjust your mixture. If your bike is idling you can vacuum sync. A carb problem would be consistent between 1st and 5th gear. As many have said so far you are perfectly describing an unsynced and rich condition. You can make a manometer out of a vacuum gauge, or two snapple bottles, etc, if thats what's making you put this off. You're talking about step 7, but you haven't done step 1-6 (and you're lucky enough to KNOW step 1-6 which is the hardest part). Get to work!!

 

and spend the money on a colortune. I found that the screws on my bike aren't the same amount of turns for the Perfect mixture

 

i have a manometer. built it last year for the bike i had last year. i've had sync problems before. but never experienced the type of problem i'm having now.

as far as the mixture screws. i've turned em up all for the highest idle. and continued turning till the idle just starts to drop. then i've tried back in just at the point the idle drops. neither way has an effect.

i'm gonna pull the carbs apart to check those emulstion tubes. then try a sync job. next chance i get. but i'm really thinking it's a spark issue.

i know i described the problem as a boggy throttle. but the more i ride it. the more i realize that it's stumbling. not boggy. teh plugs are supposed to fire every time the piston hits top dead center. but it feels like they are only firing every other time.

 

I only found my TCI to be faulty at low RPM's w/ the colortune. I hope to receive my replacement TCI today and will post the results. I was actually able to see no combustion through the colotunes' site glass and then on Big explosion every 5 strokes or so. and yes my symptom was the same as yours but at the low end, not the top end. I really didn't want to bring that up because it seemed like such a rare thing. I've been posting my problems for over a year that never came up, the colortune was the last thing i had to do before selling my 82 650 but that process opened up a new door for me. our parts are getting OLD

 

being as how i got one plug that's golden brown. and 3 that are blackly rich. i'm going to look into the plug wires. i think i would be safe in assuming that one c ylinder is running correctly. so it can't be the coils. since one coil controls two cylinders. i would s ay one wire is good and one is bad. while the other two are bad on the other coil.

i did do the plug disconnect and run motor. 2 doesn't have much effect at all. 3 has the biggest effect. and it's the one ru nning brown. 1 and 4 had the same effect. worse then 2 but not as bad as 3.

 

pulled the plugs out. cranked the motor over. 4 is most defenitly missing some beats.

looks like plug wires. so, can anyone tell me if these things just unscrew from the coil. i got the caps off. but they seem to be stuck in the coils.

 

your timing is impecable. this thread is on the main page Today

http://www.xjbikes.com/Forums/viewtopic/t=25103.html

 

ok, i've found a manual to download so now i have all the specs. jet numbers and everything. i've got the carbs completly torn down now. need a magnifying glass to make out the numbers. but the emulsion tubes check out. all holes are cleared.

i've also got the specs for the ignition system. and tested the caps ONLY.
needless to say. one of the caps has resistance that is 50 times higher then the other 3 caps. 185k ohms compared to 7-5k ohms for the other 3. haven't tested the coils yet.

 

well, whatever my problem is. it seems to smooth out quit a bit after about an hour of riding. guess i'll just live with it and see what happens.

 

what happened with the 185 Ohm caps? you can do more to solve it, carb sync, colortune

 

My 1982 xj 650 13,XXX miles is doing the same as you have described.
I called a cycle shop to get it in to have it sync-ed.
He asked about what it was doing, I told him the symptoms. He
said a sync wont help that issue. He said it was the low speed jets.
I took it all apart and the jets are clear.

Im gonna start to try this as soon as it quits raining here.


" The dead spot coming off-idle is all in the Pilot Mixture Tuning.

That dead spot could be either too Lean or too Rich.

A glance at your four Spark Plugs will solve the mystery in short order.
Since you said "Dead Spot" and NOT "Bogging" ... I'll guess that you haven't got the Pilot Mixtures RICH enough to sustain Ignition until the Main Jet Supply kicks in.

You can't be too far out of whack.
If the Plugs are looking CLEAN upon inspection ... Adjust the Pilot Mixture Screws Out ---> A LITTLE BIT!

A little bit is a TWEAK.
A TWEAK is about the width of a Nickel.
About 3 degrees.
That's all.

Commence Fine-tuning by means of Plug Chops.
Keep an eye on you Plugs and TWEAK the Mixture Screws for a Dark Tan on the Plugs.

Adjust EACH Hole independently of all others.
If a Hole looks LEAN ... Tweak it Out.
If a Hole looks RICH ... Tweak it In.

Keep a Log of what you are doing until the Plug Chop Tuning is done.
Once you get the Plugs right ... you are in the window of Fine Tuning.

An acceptably Lean Mixture will give you Hard Acceleration and Intense Engine Braking.

A Rick Mixture will give you velvety-smooth acceleration and moderate engine COASTING>

You can TWEAK the Holes for the way you need them for any particular Riding Conditions.
If you are hitting the road for a long-haul ... you want 'em on the Rich side to ride smooth and coast when you get off it.

If you are going Head Hunting and want Sport Bike Performance ... Tweak them on the Lean Side for the explosive power in acceleration and engine brbaking for the sweepers and turns.

_________________
Rick Massey
Moderator - Tech Writer

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My friend, if you think spark is to blame check all spark plugs to make sure they are firing.
1&4 AND 2&3 are paired coils.

If thats not the issue you have an AIR/FUEL issue.
If you have PODS, you have committed carb suicide
If your stocking it up, then we need to make sure your jets are correct.
Please post your pilot jet and main jet number.

If those numbers are good, we need to make sure the carbs are synced.
One slight miscalculation on the sync will cost you big time. The bike will run like crap and you will complain...."My bike dont run good" Boo hoo
Make sure the values are IDENTICAL!!! No if ands or buts.

After thats complete we can take a look at another issue. You have black plugs!!!
Those black plugs are not acceptable, thats what we call fouled. Fouled means your running rich and running rich on our air cooled bikes means stumbling...TAH DAH!!
Turn the tiny brass screws INWARDS a quarter at a time on each offending carb cylinder until the plug becomes white or golden tan. If white come back to that cylinder and turn OUTWARD until you get a golden tan.

Do not rely on a colortune or any other device. Pull the plug and see the color with your own eyes. Your eyes dont lie and black is not a color you want to see. Tan like a hawaiian goddess is more like it

 

I thank you kind sir for the advice.

I know the plugs are firing... I've pulled and brushed
the black, dry soot from them a number of times.

I guess I should verify if they ate firing with the add on
plug extender with the built in light.

Yesterdays job was to check the carbs inside and out.

Today's Job is install iridium plugs, adjust the mixture toward lean. (seemed to be the easiest step)

If this doesn't help I will compare jet numbers to my manual like you suggested.

Thanks again. Very very helpful advice.

 

No stumbling / dead spots now in throttle.
Im on my way to fine tuning this !!!

Thanks for that help !!!!


EDIT: the initial plug check showed all 4 plugs had Black chalky soot on them.

 

Love the chart!

 

Thanks!!! I got the idea from you guys. Its my second day on here and Im almost fine tuned !!!!

 

Way to go BillB !!

Welcome to the Site- - +1 on the chart for dialing it in.